Magnesium oxide powder has been used in refractory, various additives, fillers for resin, optical materials, electronic parts applications, raw materials for fluorescent material, raw materials for various target materials, raw materials for superconductor thin film undercoat, raw materials for tunnel barrier for use in tunnel magnetoresistive element (TMR element), raw materials for protective film for use in color plasma display panel (PDP), catalysts, and the like, and has drawn attention as inorganic materials having a wide variety of applications.
Patent document 1 discloses a high specific surface-area magnesium oxide powder having a BET specific surface area in the range of from 230 to 500 m2/g, wherein 80% by mass or more of the particles constituting the magnesium oxide powder are particles belonging to the undersize of a sieve having a sieve opening of 0.25 mm. Further, patent document 1 has a description that for producing the above magnesium oxide powder, magnesium hydroxide particle powder wherein the magnesium hydroxide particle powder has a BET specific surface area in the range of from 10 to 200 m2/g, wherein more than 20% by mass of the particles constituting the magnesium hydroxide powder are particles belonging to the undersize of a sieve having a sieve opening of 0.25 mm, is calcined by heating at a temperature of 250 to 550° C. under a pressure of 300 Pa or less for 1 to 10 hours.
Patent document 2 discloses that magnesium oxide having a BET specific surface area value of 5 to 150 m2/g is disintegrated by forcibly passing it in a dry state through a screen having a screen opening of 70 to 200 μm to produce magnesium oxide, the secondary particles of which have a cumulative 50% particle diameter of 2 μm or less.
Patent document 3 discloses that a magnesium oxide precursor is calcined in a closed system in the presence of halogenide ions in an amount of 0.5 to 30% by mass relative to the total mass of the precursor, to produce a magnesium oxide powder having a shape of cube and having a cumulative 5.0% particle diameter (D50) of 1.0 μm or more obtained in the measurement of laser diffraction scattering particle size distribution.